In recent years, various preservatives such as croesote, penta-petroleum and cromated copper arsenate, have been used to treat wooden poles so as to retard deterioration. Some of the preservatives appear to have a varying effect upon the hardness of the outer wood of the pole which can affect the safety of a lineman attempting to climb it. Too hard a wood can result in insufficient penetration of the lineman's gaff or spur into the side of the pole so that his foot may tear away the wood when he places his whole weight on it.
Various methods have been used in the past to test the hardness of this outer wood. For instance, a May 1972 article entitled "Is Wood Hardness Affected by Preservative Treatment?" by Robert L. Ethington, Forest Products Journal, Volume 22, No. 5, pages 60-61; describes the use of a standard ball hardness penetration test to check a number of poles treated with various preservatives. However, this test has been found to be relatively unsatisfactory in providing correlated results obtained in subjective field tests by linemen climbing the poles.
An earlier method is described in the Sept. 15, 1957 issue of Electric Light and Power in an article entitled "Treated-Pole Hardness Tested" by Henry A. Huber. Here, a conical spur is dropped down a tube mounted on the side of a standing pole at the same angle as a lineman's spur or gaff. The conical tip of the spur is graduated so that the amount of penetration into the wood can be read directly thereoff. However, a serious limitation of this device is that the tip of the spur causes a curled shaving of wood to form at the point of entry of the spur so that it is difficult to obtain an accurate reading on the amount of penetration. In addition, it cannot be readily used for checking poles during acceptance when they are lying flat on the ground.